1. Field of the Invention
The present invention relates to an electromagnetic actuator, and more particularly, to an electromagnetic actuator used for mobile phones, beepers and so on for making a call at the time of signal arrival by sound or vibration.
2. Description of the Related Art
A first electromagnetic actuator disclosed in WO No. 39843/1999 is well known as this type of electromagnetic actuator. The first electromagnetic actuator is shown in FIG. 6. As shown in FIG. 6, an electromagnetic actuator 100 includes a magnet 105 in a groove of a yoke 103 in a case 101 and a coil 109 mounted to a diaphragm 107 in the groove with a gap provided between it and the magnet 105. The yoke 103 is supported by upper and lower vibration plates 111 and 113 arranged in parallel on the side of the case 101. By applying a low-frequency current to the coil 109, the yoke 103 vibrates by the action of the vibration plates 111 and 113, and by applying a high-frequency current to the coil 109, the diaphragm 107 vibrates to generate a high-frequency sound. Also, a collar 115 projects from the case 101 in the radial direction for regulating the vibration direction of the yoke 103 in the vertical direction.
A second electromagnetic actuator of the same type uses two coils for driving, which is shown in FIG. 7. As shown in FIG. 7, an electromagnetic actuator 200 includes a vibration coil 203 and a voice coil 205. The vibration coil 203 is secured to the upper collar of a case 213 and is disposed in an external gap formed between a pole piece 209 and the external wall of a yoke 210. The voice coil 205 is secured to a diaphragm 223 and is disposed in an inner gap formed between the pole piece 209 and the inner wall of the yoke 210.
An upper leaf spring 217a is interposed between the external wall of the yoke 210 and the upper collar of the case 213; and a lower leaf spring 217b is interposed between the bottom of the yoke 210 and a cover 214 and is compressed from a natural position to support the yoke 210 by sandwiching it from above and below.
A ring-shaped magnet 207 has a pole piece 209 bonded to the top thereof, the bottom of which is secured to the concave portion of the yoke 210, and the yoke 210, the magnet 207, and the pole piece 209 form a vibration body in which the total mass thereof is supported by the spring constant of the leaf springs 217a and 217b. A direction regulating member 241 projecting from a central yoke of the cover 214 acts as a shaft for regulating the movement of the yoke 210 only in a vertical direction.
When a low-frequency current is applied to the vibration coil 203 from a terminal block 213c, the yoke 210 vibrates and, when a high-frequency current is applied to the voice coil 205, the diaphragm 223 vibrates to generate a high-frequency sound.
Furthermore, there is a third electromagnetic actuator of the same type using two coils, which is shown in FIG. 8. As shown in FIG. 8, in a third electromagnetic actuator 300, pole pieces 309a and 309b bonded to the top and the bottom of a magnet 307, respectively, face a yoke 310; a vibration coil 303 is disposed in a lower gap portion and a voice coil 305 is disposed in an upper gap portion; and the yoke 310 is sandwiched by two leaf springs 317a and 317b. 
A case 313 supports the leaf springs 317a and 317b with the inner periphery thereof, and supports a peripheral yoke of a diaphragm 323. The case 313 supports the vibration coil 303 and also supports the magnet 307 and the pole pieces 309a and 309b with a support base 315.
When a low-frequency current is applied to the vibration coil 303 from a terminal block 313c, the yoke 310 vibrate and, when a high-frequency current is applied to the voice coil 305, the diaphragm 323 vibrates to generate a high-frequency sound. Referring to FIG. 8, there is also provided a configuration in which a vertical midpoint of the yoke 310 and a vertical midpoint of the magnet 307 are connected with a ring-shaped arm (not shown) and the support base 315 is eliminated. With such a configuration, since the total math of the yoke 310, the magnet 307, and the pole pieces 309a and 309b acts as a vibration body, thus increasing vibration.
Also, referring to FIG. 8, there is also provided a configuration in which the yoke 310 is replaced with a combination of the ring-shaped magnet 307 and the pole pieces 309a and 309b, and the combination of the magnet 307 and the pole pieces 309a and 309b is replaced with the yoke 310. With such a configuration, the volume of the magnet 307 can be increased.
However, the art shown in FIG. 6 has problems in that since the collar 115 for regulating the direction of vibration is brought into contact with the yoke 103, stable vibration is lost, and that when a high-frequency current is applied to the coil 109 during the vibration of the yoke 103, distortion of a high-frequency sound is caused owing to a low-frequency vibration.
Also, the arts shown in FIGS. 7 and 8 have a problem in that when a low-frequency current is applied to the vibration coils 203 and 303, the yokes 210 and 310 vibrate and gaps in which the voice coils 205 and 305 are positioned also vibrate, and accordingly, when the simultaneous generation of a low-frequency vibration and a high-frequency sound is intended, distortion of the high-frequency sound is caused because of the low-frequency vibration.
Accordingly, it is an object of the present invention to provide a compact electromagnetic actuator capable of generating a high-frequency sound without distortion while ensuring stable vibration even during low-frequency vibration.
In order to achieve the above object, an electromagnetic actuator according to a first aspect of the present invention comprises a magnet; a pole piece mounted to the magnet; a yoke facing the pole piece; a coil base having a vibration coil facing the pole piece; a leaf spring for supporting the coil base and a weight disposed around the periphery of the yoke; a case for enclosing them; a cover for covering one side of the case; and a diaphragm having a voice coil, wherein arms of the coil base are inserted through notches formed in the yoke to allow the vibration coil and the voice coil to be disposed in a gap in which the pole piece and the yoke face each other; the weight vibrates by the application of a low-frequency current to the vibration coil; and the diaphragm vibrates by the application of a high-frequency current to the voice coil facing the pole piece.
In this invention, since the voice coil is positioned in a gap sandwiched by the fixed pole piece and the yoke, it can generate sound without the influence of vibration even during the vibration of the weight.
According to the present invention, preferably, in the above invention, the pole piece is composed of two pole pieces mounted on the top and the bottom of the magnet; the vibration coil is disposed in a lower gap portion in which the pole piece and the yoke face each other; and the voice coil is disposed in an upper gap portion.
This invention has similar advantages to those of the above invention and, since the vibration coil is disposed in the lower gap portion, induced interference between both coils can be reduced.
According to the present invention, preferably, in the above invention, the vibration coil and the voice coil are concentrically disposed in the gap in which the pole piece mounted on the top of the magnet and the yoke face each other.
This invention has similar advantages to those of the above invention and, since only one gap is formed, leakage flux can be reduced.
According to the present invention, preferably, in either of the above inventions, the leaf spring, which is composed of two leaf springs arranged close to each other, supports only one side of the weight.
This invention has similar advantages to those of either of the above inventions, and the fluctuation of spring constant can be reduced and the weight can be increased in mass. Thus, stable and larger vibration can be obtained.
According to the present invention, preferably, the cover and the yoke include fan-shaped notches and convex portions, respectively, which are fitted with each other in either of the above inventions.
This invention has similar advantages to those of either of the above inventions and, since the cover and the lower part of the yoke are fitted with each other, assembly accuracy can be improved.
According to the present invention, preferably, the two leaf springs are used as electric supply terminals in either of the above inventions.
This invention has similar advantages to those of either of the above inventions and, since the two leaf springs also act as electric supply terminals, the number of parts can be decreased.
According to the present invention, preferably, the coil base is a resin molding and insulates the two leaf springs from each other in either of the above inventions.
This invention has similar advantages to those of either of the above inventions and the two terminals can reliably be insulated from each other.
An electromagnetic actuator according to a second aspect of the present invention comprises: a magnet; a pole piece mounted to the magnet; a central yoke facing the pole piece at the center with a voice coil facing the pole piece sandwiched therebetween; a yoke facing the pole piece at the outer periphery with a vibration coil facing the pole piece sandwiched therebetween; a weight having the vibration coil and supported by a leaf spring; a case having the magnet and enclosing them; and a diaphragm having the voice coil, wherein a first magnetic circuit is formed from the pole piece toward the center via the central yoke and the case with an inner gap sandwiched therebetween; a second magnetic circuit is formed from the pole piece toward the outer periphery via the yoke and the case with an outer gap sandwiched therebetween; the weight vibrates by the application of a low-frequency current to the vibration coil; and the diaphragm vibrates by the application of a high-frequency current to the voice coil.
In this invention, since the voice coil is positioned in the inner gap sandwiched by the fixed pole piece and the central yoke, it can generate sound without the influence of vibration even during the vibration of the weight.
An electromagnetic actuator according to a third aspect of the present invention comprises: a magnet; a pole piece mounted to the magnet; a peripheral yoke facing the pole piece at the outer periphery with a voice coil facing the pole piece sandwiched therebetween; a yoke facing the pole piece at the center with a vibration coil facing the pole piece sandwiched therebetween; a weight having the vibration coil and supported by a leaf spring; a case having the magnet and enclosing them; and a diaphragm having the voice coil, wherein a first magnetic circuit is formed from the pole piece toward the outer periphery via the peripheral yoke and the case with an outer gap sandwiched therebetween; a second magnetic circuit is formed from the pole piece toward the center via the yoke and the case with an inner gap sandwiched therebetween; the weight vibrates by the application of a low-frequency current to the vibration coil; and the diaphragm vibrates by the application of a high-frequency current to the voice coil.
In this invention, since the voice coil is positioned in the outer gap sandwiched by the fixed pole piece and the peripheral yoke, it can generate sound without the influence of vibration even during the vibration of the weight.
According to the present invention, preferably, a direction regulating member is provided along the inner periphery of the weight to regulate the vibration direction of the weight in either of the above inventions.
This invention has similar advantages to those of either of the above inventions and, since the weight vibrates only in the vertical direction and the shock resistance of the configuration is improved.
According to the present invention, preferably, the weight is a molding produced by sintering high specific gravity powder in either of the above inventions.
This invention has similar advantages to those of either of the above inventions and the weight can be increased in mass and thus larger vibration can be obtained.